DESCRIPTION (Taken from the application): Gene delivery is a promising new strategy for the treatment of arthritis. Indeed, local intraarticular delivery of cDNAs encoding such proteins as IL-1Ra, vIL-10 and IL-I and TNF receptors has striking beneficial effects in animal models. However, intra-articular gene expression diminishes over a period of a few weeks, even when using vital vectors that encode no viral proteins. Until the basis for transient gene expression is understood and overcome, it will remain an impediment to effective pre-clinical development of arthritis gene therapies. This proposal is designed to test the hypothesis that intra-articular transgene expression is curtailed at least in part by immune reactions to experimental transgene products that cross gene species barriers. The rabbit knee joint is ideally suited for studies of intra-articular gene expression, and has provided much of the key data in the field to date. It is similar in size to many human joints, and permits accurate intra-articular injection and reliable lavage of the joint space. Fluids recovered from joint lavage can be used to quantitate expression of secretable gene products. And since joint lavage does not require sacrifice and can be repeated serially, it is possible to study patterns of transgene expression over time within the same animals. To bring the advantages of this model to bear upon the present hypothesis it is essential to use rabbit genes that express measurable secreted products, exist at minimal concentrations naturally and have no influence on the biology of gene expression. Currently no such reporter gene system exists. The goals of this proposal are to develop a secretable marker gene system completely native to the rabbit and to use tiffs system to establish intra-articular transgene expression profiles of three gene delivery systems with promise for clinical application. The specific aims of the proposal are 1) to clone and engineer secretable (s) monomeric form of the rabbit homologue of CD4 as a market gene product. 2) to develop a sensitive ELISA for rabbits sCD4, 3) to generate high titer retrovirus and adeno-associated virus vectors encoding rabbit sCD4, 4) to characterize the duration of intra-articular expression of rabbit sCD4 following gene transfer to the rabbit knee with each vector system. These reagents will provide essential tools for this and future studies designed to achieve long-term intra-articular gene expression.